Two-linear-polarization measurement of O 2 A band with TANSO-FTS onboard GOSAT

Transcription

1 Remote sensing in the O 2 A band Two-linear-polarization measurement of O 2 A band with TANSO-FTS onboard GOSAT July 7, 2016, De Bilt Akihiko Kuze, Hiroshi Suto, Kei Shiomi, Nobuhiro Kikuchi, Makiko Hashimoto (JAXA), Jun Yoshida (NEC), and Fumie Kataoka (RESTEC)

2 TANSO-FTS on GOSAT -2-

3 O 2 A measurement with TANSO-FTS onboard GOSAT 7 years in space Simple instrument line shape function FWHM= 0.36 cm -1 (Resolving power: cm -1 /0.36 cm -1 =37,000) close to theoretical model (Asymmetry due to finite field of view) High resolution O 2 A band data have more than one piece of information: Surface pressure, aerosol optical thickness, aerosol height. Which parameters are retrieved are assumed depends on algorithm. A. Kuze et al.: Update on GOSAT TANSO-FTS in space, July, 2016, O 2 A workshop 3 Atmos. Meas. Tech., 2016

4 FTS Optics Layout FTS multiplex advantage: exact the same IFOV: SWIR, TIR, 2 linear polarization with the secondary pointing system since Jan. 26, 2015 Much better than the primary CMOS Camera 1296 by 1040 pixels Scene flux from nadir Deep space view Black body view Primary System Diffused solar flux Pointing and image motion compensation Secondary System Aperture stop (Cube Corner) Collecting mirror Field stop DF2 DF1 DF3 Collimating mirror BPF1 BPF2 BPF3 MCT(B4) on Dewar and Pulse Tube Cooler July, 2016, O 2 A workshop Si (B1)P,S InGaAs with TE cooler (B2) P,S InGaAs with TE cooler (B3) P,S 4

5 FTS multiplex advantage improve understanding of Radiative Transfer Wide dynamic range is needed FTS covers wide spectral range SWIR: near surface information TIR and O 2 A profile information Polarization: scattering information Pointing: scattering information Stratospheric aerosol Cloud GHG Tropospheric aerosol Earth s surface High spectral resolution data of (1) Solar lines (Fraunhofer lines, Fluorescence) (2) Earth albedo (reflectance and scattering) (3) Thermal radiation (4) Two linear polarizations including O 2 A July, 2016, O 2 A workshop 5

6 Technical Challenge -6-

7 FTS Design FTS multiplex and throughput advantages (1) Diffuculty of modulation Temperature control Flat BS > 70% (2) Shorter than sampling frequency of long life diode (1.3μm) (3) Limited number of digitization bit (16 bit) Too small for dark target, difficult to predict AC sampled and non-linear center bit is frequently used. Sharp cut electric filter causes non-linearity Possibility of systematic Error (4) Sensitive to micro vibration Delay matching Re-sampling (5) Degradation on orbit by UV radiation Post launch Calibration (6) Both instrument and target are highly Polarized Mueller Matrix July, 2016, O 2 A workshop 7

8 Data processing is mainly for Non linearity correction Si Detector band1 analogue circuit I/V convertor Pre-Amplifier Unit High Gain Amplifier* Low pass filter* Low Pass Filter Unit Band pass Filter 16bit ADC* SWIR-Analog Signal Processor *Major intensity dependent phase source *Major nonlinearity source in intensity *ADC has nonlinearity but can not be corrected. Y-Axis X-Axis X-AXIS (Re-sampling) (1) FTS mechanism scan speed instability correction for medium gain (2 sinusoidal sources) (2) Sampling interval non-uniformity correction (SINUC) (3) Analogue circuit intensity dependent phase delay correction (4) Doppler shift due to image motion compensation (forward to backward viewing) (not corrected) Y-Axis (Intensity correction) (1) Intensity variation (low frequency) component correction (2) Band 4 (TIR) detector nonlinearity correction (3) Band 1 high gain amplifier nonlinearity correction (4) ADC nonlinearity (not corrected) July, 2016, O 2 A workshop 8

9 Radiometric Degradation -very slow after rapid degradation for the first 2 years- front side/ backside (1) Combination of Vicarious calibration for absolute and backside solar diffuser for relative (2) Minimizing the exposure time of the calibration sources. (3) Redundant Sahara: unknown AOT Lunar: Strong BRDF Measure all the geophysical parameters related to radiative transfer Vicarious Calibration (0.76, 1.6, 2.0 μm) July, 2016, O 2 A workshop 9

10 - Retrieved Parameters

11 Estimating light path modification using O2A band will reduce XCO2 uncertainty directly. <Parameters to be retrieved> (too many) Surface pressure Cloud or aerosol optical thickness Cloud or aerosol height Cloud fraction O2 CO2 10km O2 July, 2016, O2A workshop <Recently improved> Chlorophyll Fluorescence Line parameters Solar lines Level 1 nonlinearity correction intensity and phase <Available information not used yet> Polarization 11

12 Surface Pressure retrieved from previous Level 1 B produces To be updated from New Level 1B V201 Histograms of the residual between the retrieved surface pressure and a priori. Data time periods: NIES: 2009/06/ /07/31 ACOS: 2012/04/ /05/17 NIES v02.00 ACOS B2.9 Both NIES and ACOS data show around -5hPa difference between gain H and M with previous Level 1 versions. July, 2016, O 2 A workshop 12

13 Fluorescence and solar lines update June Frankenberg et al., GRL 2011 Toon et al., IWGGMS, 2015 July, 2016, O 2 A workshop 13

14 Aerosol Detection Sensitivity test from two linear polarizations and quasi-multi angle observations at the calibration site of Railroad Valley, NV U.S.A. Path 36 (the first day) Index R R P( in A band ) P( out of A band ) / / R R S ( in A band ) S ( out of A band ) 1 Path 37 (the following day) Index =0 in case of no aerosol/ no cloud Cloud and aerosol phase function P>>S Aerosol Optical Depth Forward scattering (path36 looking west) index vs Aeronet AOD July, 2016, O 2 A workshop Not filtered yet. 14

15 - Concludion- -15-

16 Conclusion (1) GOSAT provided well calibrated high resolution radiance spectra since (2) 7.5 years dataset (Level 1 V201) are available with onboard Camera Image. (3) XCO 2, XCH 4 retrieval have be much improved for last 7 years. However, TANSO-FTS data have not been fully used yet: synergistic use of thermal IR, polarization, multi angle. (4) Validation (especially vertical information) methods have to be investigated. JAXA EORC GOSAT home page released in May, 2016 New, status update, L1 algorithm July, 2016, O 2 A workshop 16